The Louisiana Department of Social Services was running four shelters -- two in Shreveport, one in Bastrop and one in Monroe -- holding 10,000 people, Stephens said. Some drove; others arrived by bus, train and plane, she said.

The Federal Emergency Management Agency was working with the Red Cross to run two shelters -- in Shreveport and Alexandria -- that were filled to capacity with 5,500 people, she said.

The Department of Health and Hospitals was running five medical special-needs shelters -- in Baton Rouge, Alexandria, Bossier City, Hammond and Monroe -- that were nearly full with 1,000 patients, she said.

Those figures do not include residents who sought shelter in local facilities set up by individual parishes or communities, she said.

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In Alexandria alone, the Red Cross was running about 40 shelters, a public affairs officer said.

In Mississippi, a spokesman for the state department of emergency management said that more than 12,400 evacuees, many of them from Louisiana, were staying in 97 shelters.

He said the state's six southernmost counties alone were sheltering 3,134 evacuees in 19 shelters.

Stephens said shelter organizers are asking people to remain in their shelters even after Gustav passes while damage is assessed.

"They'll let people know when it's safe to return," she said, citing post-storm threats posed by downed power lines and trees, floodwater and debris.

The National Guard said it had more than 16,000 people from more than 15 states stationed in the Gulf Coast region.

More than 7,000 National Guard troops were on emergency duty in Louisiana, with more than 2,000 of them in New Orleans alone, said Capt. Kevin Cowan. He said that figure was "about the same" as it was during Hurricane Katrina three years ago.

Though they originally focused on evacuations, late Monday afternoon they began search-and-rescue operations and anti-looting patrols, he said.

The National Guard said its work began long before Gustav hit. By Sunday, it said in a statement, Air National Guard personnel from Texas, Delaware, West Virginia, Oklahoma and Tennessee had evacuated 247 patients from Beaumont, Texas, and taken them to Lackland Air Force Base in San Antonio.

The National Guard also evacuated more than 17,000 people, including 325 special-needs patients, from New Orleans.

The Red Cross was opening two emergency shelters in East Baton Rouge Parish on Monday night. A facility at the Bethany World Prayer Center in Baker will house 300 people, and a shelter at the Breck Center will accommodate 400. A third location, to be determined, was to open Tuesday to house an additional 400 people.

On Tuesday, 500 utility workers from across the country were to arrive to help fix the parish's near-total power outage.